1. Field of the Invention
The present invention relates to an electric junction box having an improved case structure.
2. Description of the prior art
For example, an electric junction box mounted on an automobile has a configuration in which a circuit structure, having an electric circuit formed on a substrate, is accommodated within a case. The circuit structure comprises, for example, a printed circuit board, a plurality of bus bars disposed on the rear side of the printed circuit board, and a switching element such as a relay, etc., mounted onto the front side of the printed circuit board. Terminal parts formed by bending the end portions of each bus bar protrude from the peripheral portion of the circuit board. The end portions thereof are covered with a housing. On the other hand, the case comprises a frame disposed so as to surround the circuit structure along the periphery of the circuit board, a heat sink fixed onto the frame so as to be in contact with the rear side of the circuit structure from the rear side of the frame, and a cover attached to the frame from the front side to cover the circuit structure. One of such electric junction boxes is disclosed in Japanese Laid-Open Patent No. 2003-164039.
One of such electric junction boxes may have a configuration in which a portion close to the tip of a bus bar is bent substantially perpendicular to the circuit board so as to rise up toward the front side, inside of the interior of the frame. A portion, closer to the tip side than the bending part, is further bent in a horizontal direction, substantially parallel to the circuit board, so as to be directed opposite to the substrate. The tip thereof serves as a terminal part. Those terminal parts are provided in the front side of the frame.
The electric junction box having such a configuration is assembled as follows. At first, a circuit structure, in which a switching element, etc., is mounted, is incorporated in the frame so as to be inserted inside of the frame from the front side thereof, in order to avoid interference between the terminal part and the frame. Thereafter, a heat sink is bonded onto the rear side of the bus bar and the rear side of the frame. Lastly a cover is incorporated onto the front side of the frame to cover the circuit structure.
The electric junction box is provided with a bus bar and is designed to dissipate heat, generated in the bus bar as a result of conduction, to the outside via the heat sink. In order to enhance the heat dissipation efficiency thereof, the tightness of the contact between the bus bar and the heat sink, which is present on the rear side of the circuit board, is required to be enhanced. And, in order to enhance the tightness of the contact, it may become necessary that a press jig, which is used to press the circuit board and the heat sink with an adhesive sandwiched therebetween, applies a pressure over a wide range on both sides of the circuit board so as to strongly bond the bus bar and the heat sink together over the wide range.
However, in the case where a circuit structure with switching elements, which are mounted onto the circuit board as described above, is bonded to the heat sink, it is impossible to bring the press jig into contact for bonding due to the switching elements. Therefore the press jig must press locally, such as among the sides of the circuit board, only at the regions where no switching elements are disposed. Accordingly, it is impossible to strongly bond the bus bar to the heat sink over a wide range, resulting in the possibility of a drop in the heat radiation efficiency.
On the other hand, in the case where the heat sink is bonded in advance onto the circuit board and the frame, and the switching elements or the like are then mounted onto the circuit board, the heat resistance of a frame, made of synthetic resin, for example, causes a limitation for these processes, such as not allowing reflow soldering to be used for mounting the switching elements.
The present invention was completed based on the circumstances as described above. An object thereof is to provide an electric junction box that can bring the bus bars and the heat sink into a tight contact with each other over a wide range.